How do "modern"
A few crickets heard in this question. Good 'ol RTFC with some discrete event simulation papers and Wikipedia:
The algorithm used by this cron is as follows:
- On start-up, look for a file named .crontab in the home directories of all account holders.
- For each crontab file found, determine the next time in the future that each command is to be run.
- Place those commands on the Franta-Maly event list with their corresponding time and their "five field" time specifier.
- Enter main loop:
- Examine the task entry at the head of the queue, compute how far in the future it is to be run.
- Sleep for that period of time.
- On awakening and after verifying the correct time, execute the task at the head of the queue (in background) with the privileges of the user who created it.
- Determine the next time in the future to run this command and place it back on the event list at that time